Video cameras and digital still cameras generally employ a single image sensor with a color filter array to record a scene. This approach begins with a sparsely populated single-channel image in which the color information is encoded by the color filter array pattern. Subsequent interpolation of the neighboring pixel values permits the reconstruction of a complete three-channel, full-color image. One example of this process can be found in U.S. Pat. No. 5,506,619, Hamilton et al.
Under low-light imaging situations, it is advantageous to have one or more of the pixels in the color filter array unfiltered, i.e. white or panchromatic in spectral sensitivity. These panchromatic pixels have the maximum light sensitivity capability of the capture system. Employing panchromatic pixels represents a tradeoff in the capture system between light sensitivity and color spatial resolution. To this end, many four-color color filter array systems have been described. U.S. Pat. No. 6,529,239, Dyck et al. teaches a green-cyan-yellow-white pattern that is arranged as a 2×2 block that is tessellated over the surface of the sensor. U.S. Pat. No. 6,757,012, Hubina et al. discloses both a red-green-blue-white pattern and a yellow-cyan-magenta-white pattern. In both cases the colors are arranged in a 2×2 block that is tessellated over the surface of the imager. The difficulty with such systems is that only one-quarter of the pixels in the color filter array have maximum light sensitivity, thus limiting the overall low-light performance of the capture device.
To address the need of having more pixels with maximum light sensitivity in the color filter array, U.S. Patent Application Publication 2003/0210332, Frame, describes a pixel array with most of the pixels being unfiltered. Relatively few pixels are devoted to capturing color information from the scene producing a system with low color spatial resolution capability. Additionally, Frame teaches using simple linear interpolation techniques that are not responsive to, or protective of high frequency color spatial details in the image.
What is needed is color filter array with an appropriate composition of panchromatic and color pixels in order to provide both improved low-light sensitivity and improved color spatial resolution fidelity. Additionally, a method is needed to process the image data produced by such a color filter array in order to preserve and enhance panchromatic and color spatial details and ultimate produce a full-color, full-resolution image.